The present invention generally relates to a stepping motor drive apparatus which energizes a stepping motor with a high drive current for rotation and with a low hold current for holding the shaft in a present position. More particularly, the present invention is concerned with a drive system which permits a stepping motor of the type applied with reverse torque in a stop position to positively rotate in the forward direction to a new position.
Generally, a stepping motor is energized by a high drive current for rotation and with a low hold current in a stopped condition in order to avoid generation of heat and other undesired effects. A conventional stepping motor drive system drives a stepping motor from a stopped state with the hold current applied in the stop phase and then energizes the stepping motor with a drive current starting with the next phase.
This type of conventional design, however, cannot avoid displacement of the stop position of the stepping motor used as a film ribbon feed motor for example which is subjected to a torque tending to rotate the shaft in the reverse direction. The change of current from the larger drive current to the smaller hold current when the motor stops is accompanied by a reduction in the holding force causing the shaft to move in the reverse direction due to the reverse torque exerted by the film ribbon.
Where the displacement from the stop position in the reverse direction is substantial, the start-up torque for the next drive phase becomes smaller and prevents driving of the load.